The present invention is directed to a spacer for a tension member, such as a tendon for prestressed concrete, diagonal cables for a stayed girder bridge or the like, where the tendon is made up of a number of spaced parallel elements, such as steel rods, wires or strands arranged spaced radially outwardly from a center point within a tubular sheathing.
In structural design, particularly of prestressed concrete bridge structures, there is a distinction in prestressing between pretensioning and post-tensioning. Pretensioning is mostly performed as prestressing with subsequent pretensioning, where the tendons remain free to move until the concrete has set and are subsequently bonded with the structure by injecting grout or cement paste. In post-tensioning, the tendons are mainly located externally of the concrete cross-section, however, they are supported with respect to the structure. They can be inspected at any time, retensioned and possibly replaced.
The placement of completely encased tendons, particularly tendon bundles is expensive and difficult because of their great weight, therefore, such tendons are often fabricated on site. Initially, the tubular sheathing is placed which consists in the free region of the tendon, mostly of a plastics material tube, for instance, a polyethylene tube and in the anchored region of the anchorage tubes, for instance, of steel tubing connected to the plastics material tube. In the next operation, the individual elements are, in turn, installed in the tubular sheathing with the help of pushing devices and the elements are anchored in the region of the anchorages. The remaining hollow spaces or cavities between the individual elements and the tubular sheathing are injected with a hardenable material, such as cement grout, in order to assure corrosion protection. If the grout is injected prior to tensioning the individual elements, the elements must be free to move to permit the tensioning operation. To afford such movement, so-called greased strands are used as the individual elements. These are strands covered with a corrosion protective mass and encased within a protective sheathing, such as polyethylene.
With tension members of this type which extend rectilinearly between anchorages, it is sufficient, as a rule, if the order of the individual elements within a bundle is observed only in the region of the anchorages. Such an arrangement can be assured by numbering the individual elements so that the order at one anchorage conforms with that at the opposite anchorage. Generally, spacers for maintaining the order of the individual elements are not required in the intermediate region between the anchorages.
In the case of tendons passing a change in direction point, for instance in the path of a tendon with post-tensioning for adapting the tendon to the path of the bending moments within the related structural member. The ordered array of the individual elements must be maintained not only at the change in direction of points but along the full tendon length, it must also be assured that the change in direction forces developed during tensioning and, of course, during the use of the structural member, are reliably transferred to the abutments or supports provided for the structural member.